Theory of Molecular Interactions. I. Molecular Orbital Studies of Water Polymers Using a Minimal Slater-Type Basis

TLDR

Ab initio minimal‑basis LCAO‑SCF calculations were carried out to determine the energies and geometries of small water clusters, including open and cyclic polymers up to six molecules. The authors provide an all‑orientation intermolecular potential for the water dimer, identify its equilibrium geometry and force constants, find that OH···OH···OH··· chains are favored, observe significant non‑additivity of hydrogen‑bond energies, and predict cyclic structures to be most stable for trimers and larger polymers.

Abstract

Ab initio minimal basis LCAOSCF molecular orbital calculations have been performed to determine the energies and configurations of small groups of water molecules, with particular emphasis on those aspects which are relevant to the structure of liquid water. An intermolecular potential which spans the complete range of possible relative orientations for the dimer is presented. The predicted equilibrium form of the dimer is found, together with estimates of some of the intermolecular force constants. Results of calculations on both open and cyclic polymeric water structures containing up to six molecules are included. It is found that polymers having OH···OH···OH··· chains are preferred, and that hydrogen-bond energies deviate considerably from additivity. Cyclic structures are predicted to be most stable for the trimer and higher polymers.